http://bugzilla.kernel.org/show_bug.cgi?id=11750
------- Comment #11 from [EMAIL PROTECTED] 2008-11-12 03:25 -------
No, ACPI can't help. The T43 has two variants: Intel graphics, and ATI
graphics.
It doesn't have *any* ACPI standard-based brightness control, it has just
direct EC control or some proprietary mess that we haven't all the quirks
reverse engineered, yet.
The ATI graphics variant, IBM ThinkPad T43/p model 26xx, has EC-based
brightness control. You adjust an EC register, that makes it select an
internal table of parameters to send to a PWM channel that drives the inverter
for the CCFL. This requires pure-EC, or EC+UCMS ("CMOS") control of the
backlight, performed by thinkpad-acpi.
On the Intel graphics variant, it could be either EC-based or GPU-based. Nobody
offered to help me find it out yet, and the test is simple...
Other thinkpads with ATI or Intel graphics might need just the CMOS mode and do
the EC programming in SMM in response to the SMI trap generated by the "CMOS
mode" (which, in the T43 26xx, just updates the NVRAM as far as I can see...
but we might be missing some magic that would cause it to behave like the T42).
I would really need to add intelligent state-machine-based autodetection for
this, or I'd need extensive cooperation from users of many models of old
ThinkPads to do it without the autodetection. It is not simple, and it is
error-prone.
For autodetection, one blacklist every Lenovo thinkpad to require ACPI or use
the CMOS method (none of them seem to need EC). Then one needs to check if
CMOS and EC matches. If not, use CMOS (and inform users to notify by email if
broken). If they match, lock down all brightness control from userspace, and
issue a CMOS command to increase brightness. If about 1s later the EC register
changed, use just CMOS. Otherwise, sync EC and use CMOS+EC. Unlock down
brightness control. Inform user of the autodetected mode, and request
information if it doesn't work.
As you see, it is sort of fragile and not "transparent" to the user (it WILL
need to try to mess with the backlight level). It is in my TODO list, but at a
low priority.
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